Multi-material heat exchanger construction

ABSTRACT

A recuperative heat exchanger in which the material composition of the fins and plates varies in the flow direction of the higher temperature fluid according to the designed temperature and stress conditions. A first plate of high stress- and heatresistance quality material is welded edgewise to a second plate of lower stress- and heat-resistance quality material which in turn may be edge-welded to another plate of still lesser quality material. The resulting multi-material plate is then rolled to a desired thickness and formed to provide the particular heat exchanger element. A plurality of such elements, formed as plates and fins for example, are then fabricated into a unitary heat exchanger core and arranged in a position whereby the portions of the elements having the high stress- and heat-resistance qualities are at the higher temperature end of the heat exchanger.

United States Patent Parker 1 1 Apr. 29, 1975 [75] Inventor: Kenneth 0.Parker, Rolling Hills Estates. Calif.

[73] Assignee: The Garrett Corporation. Los

Angeles. Calif.

[22] Filed: July 25, 1973 [21] Appl. No.1 382,465

[52] U.S. Cl. 165/166; [65/180129/1966: 148/127; 29/1573 D 1511 1nt.Cl.1 28b 21/08 [581 Field 01 Search 29/1966; 165/166. 180; 148/127 [561References Cited UNITED STATES PATENTS 2,464,735 3/1949 Vantlerweil165/180 2.769.227 11/1956 Sykes et ul 2.952.445 9/1960 Latld 165/1663.731.738 5/1973 Cooper 29/1966 X Primary E.\'ummerManuel A, AntonakasAss/stun! Exam/ner-Theophil W. Streule. Jr. Attorney. Agent. orFz'rmHenr M. Bissell [57] ABSTRACT A recuperative heat exchanger inwhich the material composition of the fins and plates varies in the flowdirection of the higher temperature fluid acCording to the designedtemperature and stress conditions. A first plate of high stressandheat-resistance quality material is welded edgewise to a second plate oflower stressand heatresistance quality material which in turn may beedge-welded to another plate of still lesser quality material. Theresulting multi-material plate is then rolled to a desired thickness andformed to provide the particular heat exchanger element, A plurality ofsuch elements. formed as plates and fins for example. are thenfabricated into a unitary heat exchanger core and arranged in a positionwhereby the portions of the elements having the high stressandheat-resistance qualities are at the higher temperature end of the heatexchanger.

4 Claims, 4 Drawing Figures PMENTEB APRZQ 1975 SHEEI 10F 2 AHQlN .llll'MULTI-MATERIAL HEAT EXCHANGER CONSTRUCTION BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates torecuperative heat exchangers and in particular to the construction ofsuch devices with plates of dissimilar materials.

2. Description of the Prior Art Heat exchangers of the plate type haveplates of relatively thin material formed and stacked to provide heattransfer through the plates between adjacent series of flow passages,containing fins. formed between adjacent plates. In a typicalcounter-flow heat exchanger. flow of the high temperature fluid proceedsfrom the input end which may receive. for example. hot exhaust gasesfrom a gas turbine engine. through the heat exchanger core with thetemperature of the gases continuously falling as the heat is transferredto the low temperature fluid. Accordingly. the temperature of the platesand fins of the heat exchanger core varies in the flow direction fromthe high temperature input end to the low temperature output end. Theresulting thermal gradient causes the stress levels on the plate andfins to vary throughout the core matrix with the highest stressesoccurring at the high temperature input end and the lowest stressesoccurring at the low temperature output end. The high stresses at theinput end tend to decrease the life of the core elements whereas lowstresses at the output end have less effect on the materials. Inaddition to the thermal stresses the high temperatures at the input endtend to oxidize and otherwise corrode the core parts.

In the present day design of heat exchangers. the core materials may beselected to conform to the higher stresses at the high temperature inputend thereby providing a recuperator of longer life but at considerablematerial costv In a sense this is somewhat wasteful because the costly.high quality material at the input end is not required at the lowtemperature output end. Therefore the expensive material is essentiallywasted at the low temperature end. On the other hand. if the heatexchanger is designed of material having low thermal stress quality atthe high temperature ends. the stress will exceed the yield strength ofthe low temperature material and thereby reduce the life of the heatexchanger.

Various attempts in the prior art have been made to overcome theaforementioned design requirement of a higher quality material at thehigh temperature input end and a lower quality material at the lowtemperature output end. One common approach utilizes a plurality of heatexchangers in series with the first heat exchanger receiving the exhaustgas at its highest temperature. and accordingly being designed to havehigh quality material. The next heat exchanger in the line isconstructed of lower quality material and so on. While this type ofdesign may provide a partial solution to the problem. such combinedunits are still costly and occupy more space because several differentheat exchangers are required. each duplicating the components of theother exchangers. Moreover. such an approach is particularlyinappropriate to the special manifolding configurations of integralmanifold. counter-flow heat exchangers now being designed.

Accordingly. it is a primary object of the present invention to providea heat exchanger core and specific components thereof fabricated ofmaterials which vary in heat-and stress-resistance qualities accordingto the different temperature and thermal stress conditions encounteredin the core.

SUMMARY OF THE INVENTION Briefly. according to a preferred embodiment ofthe invention a counter-flow heat exchanger core is formed of plateshaving dissimilar material compositions resulting in different thermalstressand heat-resistance qualities. Associated fin elements may also beso formed. if desired. The dissimilar material portions are first weldedtogether and then rolled to provide a desired thickness prior tofabrication in conventional manner. The resulting multi-materialelements may be positioned in a heat exchanger with the portion havinghigh heatand stress-resistance properties being at the high temperatureend of the heat exchanger and the portion of the low heatandstress-resistance properties being at the low temperature end of theheat exchanger.

In this manner the desired objective of heatand stress-resistancequalities and low overall cost of the heat exchanger can be achievedwith the quality of the material corresponding to the stresses it issubjected to.

The primary object of this invention is therefore to provide a singleunitary p e structure formed from plate sections of dissimilar mater'als with a plurality of such plates fabricated in a counter-flow heatexchanger such that the portions of highest quality are placed near thehigh temperature and thermal stress end of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the presentinvention may be had from a consideration of the following detaileddescription. taken in conjunction with the accompanying drawing. inwhich:

FIG. I is a fragmentary view of a particular counterflow heat exchangercore fabricated in accordance with the paresent invention;

FIG. 2 is a sectional view of a portion of the heat exchanger of FIG. I,taken along the lines 2-2 thereof and looking in the direction of thearrows;

FIG. 3 is a plan view of a particular heat exchanger plate fashioned inaccordance with the present invention; and

FIG. 4 is a view showing a particular method of fabrication of the plateof FIG. 3 in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. I and 2 illustrate detailsof construction of a particular type of counter-flow heat exchanger core[0 fabricated in accordance with the present invention. As shown inthese figures. the heat exchanger core 10 is made up of a plurality ofindividual plates separated by fins in known fashion. Each individualplate [2 serves as a divider sheet between adjacent streams of hotexhaust gas. as from a turbine. and cooler air driven by a compressor.In the counter-flow arrangement of FIG. I. the exhaust gas is shownflowing straight through the gas passages whereas the air is transportedto and from the various interspersed air layers by means of integralmanifolds l4 and headers 16. Thus. the heat exchanger 10 of FIG. Icomprises a sandwich structure of alternatc layers of fluid channels.half of the channels providing straighbthrough passages for the exhaustgas and the remainder providing passages between the manifold portions14 with the flow in adjacent gas and air passages being arranged inopposed directions.

In counter-flow heat exchangers. the side at which the exhaust gasenters and the heated air leaves is the hot side. whereas the oppositeside where the air to be heated enters and the exhaust gas lea\es is thecool side. As a result of the present invention. it therefore becomespossible to fabricate the respective divider sheets of plates ofsections of different materials which are welded together to form asingle plate. FIG. 3 illus trates a metal sheet 13 having three sections20. 22. and 24 joined together by weld lines 26. The sections 20. 22 and24 extend across the sheet 13 in a direction generally orthogonal to theflow direction of the coun ter-tlow fluids. Thus. the section 20comprises a material which is particularly selected for qualities ofhigh stress resistance and heat resistance. A particular material whichis suited for this section 20 is Inconel 625. The section 24 at the coolside of the sheet 13 may he fabricated of a lower cost steel such as SAEI020 steel which has lower stressand heat-resistance qualities andaccordingly is much cheaper than the material of the section 20.Intermediat sections such as 22 are operated at some temp e between thehot and cold temperatures at op osue ends of the heat exchanger core andmay be fabricated of material having intermediate stressandheabresistance qualities. such as (RFR 347.

Sheets such as that shown in FIG. 3 are trimmed and shaped to form thedivider plates I2 of FIG. 2 and fabricatcd into the heat exchanger coreof FIG. I. If desired. sheets 13 of FIG. 3 may also be fabricated intothe separator tins of FIG. 2 which are fitted between adjacent dividerplates I2. Alternatively, the finned sections may be separated at thejuncture line between adjacent plate sections 20.22 and 24 and selectedfrom respective materials matched to meet the design requirements of thetemperatures encountered in these sections.

As shown in FIG. I. such a construction in accordance with the presentinvention ofthe heat exchanger core results in a single heat exchangercore having materials selected for the various sections thereof to meetthe temperature and stress requirements to be encountered in theparticular sections. Heretoforc. those efforts directed toward realizingeconomy of manufacture for heat exchangers have resulted in a pluralityof heat exchangers interconnected in series. These have comprisedcross-flow heat exchangers strung out in line with manifolds tortuouslydirecting the flow of one of the fluids to and from adjacent sections ina serpentine manifold arrangement. The present invention avoids suchmanifolding problems by fabrication of the various sections comprisingdifferent materials in a single integrated unit.

FIG. 4 illustrates in schematic form a method of fabrication of sheetssuch as are employed in the practice of the present invention. As shownin FIG. 4. a pair of sheets and 22 of dissimilar materials are beingfabricated to form a single sheet comprising two sections of differentmaterials. The separate sheets 20 and 22 begin from rolls and 32respectively and are drawn through guide rollers 34 to a positionunderneath a welding head where the adjacent edges are butt weldedtogether. If desired. the butt weld edges prior to the welding step maybe prepared by suitable bevelling. smoothing and cleaning operations.After being edgewelded by the welding head 36. the combined sheets.joined by the butt weld 38. are passed along guided by additional guiderollers 40 to a planisher 42 having rollers 44 above and below thejoined sheets 20. 22 where the butt weld 38 is pressed and shaped to thedimension of the sheets 20, 22. From the planisher 42. the sheet istransported to an annealing oven 46. Additional rolling or planishingand annealing steps may be incorporated if desired. Finally. the sheet26 is rolled up into a roll 48 for storage until needed for cutting andtrimming to form the sheets such as l3 of FIGS. 2 and 3. Although FIG. 4shows only two sheets being welded together. additional strip stock of athird material may be joined by incorporating one more coil and one morewelding head.

Although there have been described above specific arrangements of amulti-material heat exchanger structure and methods of fabricationthereof in accordance with the invention for the purpose of illustratingthe manner in which the invention may be used to advantage. it will beappreciated that the invention is not limited thereto. Accordingly. anyand all modifications. variations or equivalent arrangements which mayoccur to those skilled in the art should be considered to be within thescope of the invention.

What is claimed is:

l. A heat exchanger core of the counterflow fluid type wherein one ofthe fluids is introduced to and removed from the core in a directionorthogonal to the direction of fluid flow through the core. comprising:

a plurality ofstacked plates formed to define layered passages for fluidstreams flowing between opposite cnds ofthe core. adjacent pairs of saidstreams being arranged to flow in opposed directions, one of said pairof streams comprising a hot gas and the other being a fluid entering thecore at a cooler temperature;

each of said plates comprising sections of different materials havingdifferent stressand heatresistance qualities. said sections beingedgewelded together along juncture lines between adjacent sections. thesections and welded edges extending transversely to the direction offluid flow through the core;

said plates being disposed within the heat exchanger such that thesections of highest stressand heatresistance qualities are locatedadjacent the hot gas inlet end of the heat exchanger core and thesections of lowest stressand heat-resistance qualities are locatedadjacent the inlet end of the cooler temperature fluid.

2. A heat exchanger core in accordance with claim I further comprising aplurality of finned elements indi vidually arrayed between adjacentpairs of plates defining said passages.

3. A heat exchanger core in accordance with claim 2 wherein said finnedelements comprise sections of different materials respectivelycorresponding in stressand heat-resistance qualities to adjacent platesections. the different finned element sections extending transverselyto the direction of fluid flow through the core and generallycoextensively with the adjacent plate sections ofcorresponding stressandheat-resistance qualities.

4. A heat exchanger core in accordance with claim 3 wherein said finnedelements adjacent sections are edge-welded together to form integralunits.

1. A heat exchanger core of the counterflow fluid type wherein one ofthe fluids is introduced to and removed from the core in a directionorthogonal to the direction of fluid flow through the core, comprising:a plurality of stacked plates formed to define layered passages forfluid streams flowing between opposite ends of the core, adjacent pairsof said streams being arranged to flow in opposed directions, one ofsaid pair of streams comprising a hot gas and the other being a fluidentering the core at a cooler temperature; each of said platescomprising sections of different materials having different stress- andheat-resistance qualities, said sections being edge-welded togetheralong juncture lines between adjacent sections, the sections and weldededges extending transversely to the direction of fluid flow through thecore; said plates being disposed within the heat exchanger such that thesections of highest stress- and heat-resistance qualities are locatedadjacent the hot gas inlet end of the heat exchanger core and thesections of lowest stress- and heatresistance qualities are locatedadjacent the inlet end of the cooler temperature fluid.
 2. A heatexchanger core in accordance with claim 1 further comprising a pluralityof finned elements individually arrayed between adjacent pairs of platesdefining said passages.
 3. A heat exchanger core in accordance withclaim 2 wherein said finned elements comprise sections of differentmaterials respectively corresponding in stress-and heat-resistancequalities to adjacent plate sections, the different finned elementsections extending transversely to the direction of fluid flow throughthe core and generally coextensively with the adjacent plate sections ofcorresponding stress- and heat-resistance qualities.
 4. A heat exchangercore in accordance with claim 3 wherein said finned elements adjacentsections are edge-welded together to form integral units.